1. Field of the Invention
The present invention relates to a variable drive current driver circuit.
2. Description of the Prior Art
According to the conventional standards, such as IEEE 1394 standards, a drive current of a signal transmitted between electronic devices, such as personal computers, video movies, or mini-disc players, connected mutually via a cable or the like is determined so as to become either of two kinds. When a certain electronic device is connected to another electronic device via a cable, the former have the latter notify the former of the standard of a signal that can be received by the latter, and the former transmits data with a drive current determined on the basis of this notification.
FIG. 1 is a diagram showing a conventional driver circuit that is capable of varying a drive current of a signal. In the conventional technique, as shown in FIG. 1, a driver circuit for either a standard A or a standard B is driven on the basis of, for example, a control signal of “0” or “1,” so as to be able to cope where the electronic device of the opposite party receives a signal of either of the two kinds of drive current defined by the standard.
In other words, if a control signal of “1” is inputted to the standard A driver circuit and the standard B driver circuit, then the standard A driver circuit is enabled and the standard B driver circuit is disabled. If a control signal of “0” is inputted to the standard A driver circuit and the standard B driver circuit, then the standard A driver circuit is disabled and the standard B driver circuit is enabled.
In the conventional technique, however, it is necessary to prepare as many driver circuits as the number of kinds of the driver current defined by the standard. As a result, the circuit scale becomes large as the number of kinds of the drive current increases, especially in an electronic device, where transmission and reception of a plurality of data are performed using one physical layer LSI, it is especially desired to prevent the circuit scale from becoming large.